The Universal Mobile Telecommunications System (UMTS) is a third generation (3G) mobile cellular system for networks based on the GSM standard. Developed and maintained by the 3GPP (3rd Generation Partnership Project), UMTS is a component of the International Telecommunications Union IMT-2000 standard set and compares with the CDMA2000 standard set for networks based on the competing 3G cdmaOne technology. UMTS uses wideband code division multiple access (W-CDMA) radio access technology (RAT) to offer greater spectral efficiency and bandwidth to mobile network operators. UMTS uses an interface called Iub between the cellular base station and the radio network controller (RNC) in the core network, which enables the RNC to perform the majority of required functions, and for the cellular base station, or nodeB, to perform primarily radio transceive, baseband and analog-digital conversion functions.
A femtocell is a small, low-power cellular base station, typically designed for use in a home or small business. A broader term which is more widespread in the industry is small cell, with femtocell as a subset. A femtocell may connect to the service provider's network via broadband (such as DSL or cable); typical designs support four to eight simultaneously active mobile phones in a residential setting depending on version number and femtocell hardware, and eight to 16 mobile phones in enterprise settings. A femtocell allows service providers to extend service coverage indoors or at the cell edge, especially where access would otherwise be limited or unavailable. Although much attention is focused on WCDMA, the concept is applicable to all standards, including GSM, CDMA2000, TD-SCDMA, WiMAX and LTE solutions.
The key interface in femtocell architectures is that between the femtocells and the femtocell gateway. Standardisation enables a wider choice of femtocell products to be used with any gateway, increasing competitive pressure and driving costs down. For the common WCDMA femtocells, this is defined as the Iuh interface. In the Iuh architecture, the femtocell gateway sits between the femtocell and the core network and performs the necessary translations to ensure the femtocells appear as a radio network controller (RNC) to existing mobile switching centres (MSCs). Each femtocell talks to the femtocell gateway and femtocell gateways talk to the Core Network Elements (CNE) (MSC for circuit-switched calls, SGSN for packet-switched calls).